In the most general terms a magnetic memory storage device consists essentially of two fundamental units, viz., a head pad or slider and a rigid information disk. The head pad supports an element which is capable of reading or writing data magnetically on the information disk; the latter consisting essentially of two basic components, viz., a rigid substrate (conventionally aluminum metal) and a coating of magnetic media on the surface thereof facing the head pad.
The market for rigid magnetic storage is well established and growing, with even greater advances being foreseen through the utilization of thin film media technology. Increased information densities, higher disk rotation speeds, and lower head flying heights not only afford greater efficiencies in data storage and retrieval, but also demand extremely tight tolerances to be held in the substrate specifications for flatness, rigidity at high rotational velocities, and surface texture. Where the product is designed for the high performance market, high capacity and rapid access characteristics are key requirements. Moreover, the current trend toward smaller disk drives and less powerful motors, particularly for the rapidly developing markets for slimline and portable drives, calls for thin, lightweight, rugged disks that have high functional densities and are capable of withstanding frequent takeoffs and landings with no deterioration in performance. The standard aluminum metal disk has difficulty meeting those enhanced performance requirements at a competitive cost.
As noted above, rigid disk substrates designed for high performance applications must meet a wide range of criteria. To illustrate:
(a) the substrates must meet stringent requirements for flatness (for example, a disk having an outside diameter of 95 mm cannot be as much as 10 microns out of flat across its diameter and should have concentricity within 50 microns); PA1 (b) the substrate should have a defect-free, non-porous surface which will also preferably be highly resistant to scratches; PA1 (c) the substrate material should be strong and sufficiently rigid to allow the fabrication of very thin disks (&lt;1 mm thickness) which are dimensionally stable during speeds of rotation up to 7200 rpm; PA1 (d) the surface of the substrate needs a slight uniform texture, i.e., an average roughness of about 1.5-6 nm, in order to provide a suitably low coefficient of "stiction," which is a measure of the interaction between a head and the disk; a low coefficient leads to improved media wear characteristics and improved start/stop characteristics; PA1 (e) the substrate material should be corrosion resistant and compatible with magnetic media; PA1 (f) the substrate should demonstrate a high surface hardness to resist scratching and damage resulting from head slap; the latter feature being especially important in portable drives; PA1 (g) the substrate should exhibit good thermal hardness to permit the deposition of thin films thereon at elevated temperatures resulting in better film deposition and higher coercivity magnetics; PA1 (h) the substrate will be re-workable; i.e., be capable of being re-used upon removal of the magnetic media coatings; and, finally, PA1 (i) the substrate disks must be extremely reliable, be of consistent high quality, and be able to be manufactured at a competitive cost.
Accordingly, the overriding objective of the present invention was to improve the performance of magnetic memory storage devices. And in order to achieve that overriding objective, a specifically-defined objective of the present invention was to fabricate rigid information disks wherein the substrate component thereof would satisfy each of the above-cited criteria .